<template>
  <scroll class="listview" 
            :data="data" 
            ref="listview" 
            :listenScroll="listenScroll"
            :probeType="probeType"
            @scroll="scroll"
            >
      <ul>
          <li  v-for="(group,groupx,groupk) in data" class="list-group" ref="listgroup" :key="groupk">
            <h2 class="list-group-title">{{group.title}}</h2>
            <ul>
                <li  @click="selectItem(item)" v-for="(item,index,key) in group.items" class="list-group-item" :key="key">
                    <img v-lazy="item.avatar" class="avatar" alt="">

                    <span class="name">{{item.name}}</span>
                </li>
            </ul>
          </li>
      </ul>
      <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
          <ul>
              <li v-for="(item,index,key) in shortcutList" 
              :data-index="index" 
              class="item" 
               :key="key"
               :class="{'current':currentIndex===index}"
               >
                  {{item}}
              </li>
          </ul>
      </div>
      <div class="list-fixed" ref="fixed" v-show="fixedTitle">
        <h2 class="fixed-title">{{fixedTitle}}</h2>
      </div>
      <div v-show="!data.length">
        <loading></loading>
      </div>

  </scroll>
</template>

<script>
import Scroll from "base/scroll/scroll";
import { getData } from "common/js/dom";
import Loading from 'base/loading/loading';
const ANCHOR_HEIGHT = 18;
const TITLE_HEIGHT = 30
export default {
  created() {
    this.touch = {};
    this.listenScroll = true;
    this.listenHeight = [];
    this.probeType = 3;
  },
  data() {
    return {
      scrollY: -1,
      currentIndex: 0,
      diff: -1
    };
  },
  props: {
    data: {
      typr: Array,
      default: []
    }
  },
  computed: {
    shortcutList() {
      return this.data.map(group => {
        return group.title.substr(0, 1);
      });
    },
    fixedTitle(){
      if(this.scrollY>0){
        return
      }

      return this.data[this.currentIndex]?this.data[this.currentIndex].title : ''
    }
  },
  methods: {
    selectItem(item) {
        this.$emit('select', item)
    },
    onShortcutTouchStart(e) {
      let anchorIndex = parseInt(getData(e.target, "index"));
      let firstTouch = e.touches[0];
      this.touch.y1 = firstTouch.pageY;
      this.touch.anchorIndex = anchorIndex;
      this.$refs.listview.scrollToElement(this.$refs.listgroup[anchorIndex], 0);
      this._scrollTo(anchorIndex);
    },
    onShortcutTouchMove(e) {
      let firstTouch = e.touches[0];
      this.touch.y2 = firstTouch.pageY;
      let delta = ((this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT) | 0;
      let anchorIndex = this.touch.anchorIndex + delta;

      this._scrollTo(anchorIndex);
    },
    scroll(pos) {
      this.scrollY = pos.y;
    },
    _scrollTo(index) {
        if(!index&&index!==0){
            return
        }
        if(index<0){
            index=0
        }else if(index>this.listenHeight.length-2){
            index=this.listenHeight.length-2;
        }
        this.scrollY = -this.listenHeight[index];
        console.log(index);
      this.$refs.listview.scrollToElement(this.$refs.listgroup[index], 0);
    },
    _calculageHeight() {
      this.listenHeight = [];
      const list = this.$refs.listgroup;
      let height = 0;
      this.listenHeight.push(height);
      for (let i = 0; i < list.length; i++) {
        let item = list[i];
        height += item.clientHeight;
        this.listenHeight.push(height);
      }
    }
  },
  watch: {
    data() {
      setTimeout(() => {
        this._calculageHeight();
      }, 20);
    },
    scrollY(newY) {
      const listenHeight = this.listenHeight;
        //当滚动到顶部，newY>0
        if(newY>0){
            this.currentIndex = 0;
            return;
        } 
        //中间部分滚动
      for (let i = 0; i < listenHeight.length; i++) {
        let height1 = listenHeight[i];
        let height2 = listenHeight[i + 1];
        if (-newY >= height1 && -newY < height2) {
          this.currentIndex = i;
          this.diff = height2 + newY;
          return;
        }
      }

        //滚动到底部

        this.currentIndex=listenHeight.length-2;
        this.currentIndex = 0;
    },
  
    diff(newVal) {
        let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
        if (this.fixedTop === fixedTop) {
          return
        }
        this.fixedTop = fixedTop
        this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
      }

  },
  components: {
    Scroll,Loading
  }
};
</script>

// <style lang="scss" scoped="" type="text/css">
.listview {
  position: relative;
  width: 100%;
  height: 100%;
  overflow: hidden;
  background: #333;
  .list-group {
    padding-bottom: 30px;
    .list-group-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
      background-color: #555555;
    }
    .list-group-item {
      display: flex;
      align-items: center;
      padding: 20px 0 0 30px;
      .avatar {
        width: 50px;
        height: 50px;
        border-radius: 50%;
      }
      .name {
        margin-left: 20px;
        color: #fff;
        font-size: 12px;
      }
    }
  }
  .list-shortcut {
    position: absolute;
    z-index: 30;
    right: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 20px;
    padding: 20px 0;
    border-radius: 10px;
    text-align: center;
    font-family: Helvetica;
    color: #ccc;
    .item {
      padding: 3px;
      line-height: 1;
      list-style: none;
       &.current{
          color: red}
    }
  }

  .list-fixed {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    background: #555555;
    font-size: 12px;
    .fixed-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
    }
  }

  .loading-container {
    position: absolute;
    width: 100%;
    top: 50%;
    transform: translateY(-50%);
  }
}
</style>
